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- /* Copyright (C) 2002, 2007, 2009 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
- Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, see
- <http://www.gnu.org/licenses/>. */
- #include "pthreadP.h"
- #include <bits/kernel-features.h>
- #include <string.h>
- static const struct pthread_rwlockattr default_attr =
- {
- .lockkind = PTHREAD_RWLOCK_DEFAULT_NP,
- .pshared = PTHREAD_PROCESS_PRIVATE
- };
- int
- __pthread_rwlock_init (
- pthread_rwlock_t *rwlock,
- const pthread_rwlockattr_t *attr)
- {
- const struct pthread_rwlockattr *iattr;
- iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_attr;
- memset (rwlock, '\0', sizeof (*rwlock));
- rwlock->__data.__flags
- = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
- /* The __SHARED field is computed to minimize the work that needs to
- be done while handling the futex. There are two inputs: the
- availability of private futexes and whether the rwlock is shared
- or private. Unfortunately the value of a private rwlock is
- fixed: it must be zero. The PRIVATE_FUTEX flag has the value
- 0x80 in case private futexes are available and zero otherwise.
- This leads to the following table:
- | pshared | result
- | shared private | shared private |
- ------------+-----------------+-----------------+
- !avail 0 | 0 0 | 0 0 |
- avail 0x80 | 0x80 0 | 0 0x80 |
- If the pshared value is in locking functions XORed with avail
- we get the expected result. */
- #ifdef __ASSUME_PRIVATE_FUTEX
- rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
- ? 0 : FUTEX_PRIVATE_FLAG);
- #else
- rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
- ? 0
- : THREAD_GETMEM (THREAD_SELF,
- header.private_futex));
- #endif
- return 0;
- }
- strong_alias (__pthread_rwlock_init, pthread_rwlock_init)
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